In recent years, with advance in digital technology, electronic devices such as mobile information devices and information home appliances have been developed to provide higher functionality. As the electronic devices provide higher functionality, miniaturization and an increase in speed of semiconductor devices for use with the electronic devices are making rapid progress. Among them, the use of large capacity nonvolatile memory, represented by flash memory, is rapidly expanding. Furthermore, as a next-generation new nonvolatile memory replacing the flash memory, there is on-going research and development of nonvolatile memory elements using what is called a variable resistance element (for example, see WO2008/149484, WO2008/146461, and WO2010/38423). Here, the variable resistance element refers to an element which has a characteristic in which a resistance value reversibly changes depending on electric signals, and further is able to store information corresponding to the resistance value in a nonvolatile fashion.
WO2008/149484 discloses a variable resistance element using, as a variable resistance layer, a stack of tantalum oxide layers having different oxygen content percentages. The variable resistance element disclosed in WO2008/149484 is formed including a first electrode layer, a first variable resistance layer comprising a tantalum oxide TaOx, a second variable resistance layer comprising a tantalum oxide Ta2O5, and a second electrode layer.
WO2008/146461 discloses a variable resistance element using the oxygen- and/or nitrogen-deficient tantalum oxynitride TaON for a variable resistance layer. The variable resistance element disclosed in WO2008/146461 includes a first electrode layer, a variable resistance layer (TaON) comprising an oxide that contains Ta and nitrogen, and a second electrode layer. WO2008/146461 discloses that a ratio of oxygen content percentage to nitrogen in the variable resistance layer (TaON) is, by way of example, equal to or greater than 1.08 and equal to or less than 1.35.
WO2010/38423 discloses a variable resistance element using a variable resistance layer having a three-layer structure in which a tantalum oxide Ta2O5, a tantalum oxynitride TaON, and the tantalum oxide TaOx are stacked in the stated order. In this structure, the tantalum oxynitride TaON is formed as a barrier layer to prevent introduction of oxygen into the tantalum oxide TaOx.
As will be described, through intensive studies by the inventors of the present invention, there are findings that conventional variable resistance elements have problems that the resistance change characteristics may deteriorate depending on a thermal budget or the like, and the stable operation at low voltages is difficult.